/*
* Copyright [2021] JD.com, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

#include "da_hashkit.h"

#define mix(a,b,c) \
{ \
      a=a-b;  a=a-c;  a=a^(c>>13); \
      b=b-c;  b=b-a;  b=b^(a<<8);  \
      c=c-a;  c=c-b;  c=c^(b>>13); \
      a=a-b;  a=a-c;  a=a^(c>>12); \
      b=b-c;  b=b-a;  b=b^(a<<16); \
      c=c-a;  c=c-b;  c=c^(b>>5);  \
      a=a-b;  a=a-c;  a=a^(c>>3);  \
      b=b-c;  b=b-a;  b=b^(a<<10); \
      c=c-a;  c=c-b;  c=c^(b>>15); \
}

typedef uint32_t u4;

uint32_t hash_chash(const char *k, size_t length)
{
	uint32_t a,b,c;  /* the internal state */
	    u4          len;    /* how many key bytes still need mixing */

	    /* Set up the internal state */
	    len = length;
	    a = b = 0x9e3779b9;  /* the golden ratio; an arbitrary value */
	    // 'TMJR'
	    c = 0x544D4A52;     /* variable initialization of internal state */

	    /*---------------------------------------- handle most of the key */
	    while (len >= 12)
	    {
	        a=a+(k[0]+((u4)k[1]<<8)+((u4)k[2]<<16) +((u4)k[3]<<24));
	        b=b+(k[4]+((u4)k[5]<<8)+((u4)k[6]<<16) +((u4)k[7]<<24));
	        c=c+(k[8]+((u4)k[9]<<8)+((u4)k[10]<<16)+((u4)k[11]<<24));
	        mix(a,b,c);
	        k = k+12; len = len-12;
	    }

	    /*------------------------------------- handle the last 11 bytes */
	    c = c+length;
	    switch(len)              /* all the case statements fall through */
	    {
	    case 11: c=c+((u4)k[10]<<24);
	    case 10: c=c+((u4)k[9]<<16);
	    case 9 : c=c+((u4)k[8]<<8);
	             /* the first byte of c is reserved for the length */
	    case 8 : b=b+((u4)k[7]<<24);
	    case 7 : b=b+((u4)k[6]<<16);
	    case 6 : b=b+((u4)k[5]<<8);
	    case 5 : b=b+k[4];
	    case 4 : a=a+((u4)k[3]<<24);
	    case 3 : a=a+((u4)k[2]<<16);
	    case 2 : a=a+((u4)k[1]<<8);
	    case 1 : a=a+k[0];
	             /* case 0: nothing left to add */
	    }
	    mix(a,b,c);
	    /*-------------------------------------------- report the result */
	    return c;
}
